1. Field of Invention
This invention relates to novel isolated Pseudomonas fluorescens strains that have been isolated, selected, and characterized from the naturally occurring soil bacterial populations because they inhibit the growth of annual bluegrass (Poa annua L.) or inhibit the growth of both annual bluegrass (Poa annua L.) and rough bluegrass (Poa trivialis), but do not inhibit the growth of desired grasses, such as turfgrasses, cereal crops, and native plants. This invention also relates to novel compositions that contain the novel Pseudomonas fluorescens strains described herein. In addition this invention relates to methods of using the novel, isolated P. fluorescens strains and the novel compositions, alone or in combination with other P. fluorescens strains, herbicides, and/or fertilizers.
2. Description of the Prior Art
Annual bluegrass (Poa annua L.) is a cool-season annual grass that is a major weed species in turf, turfgrass seed production, and golf courses of the western United States (Webster and Nichols, 2012 Weed Science 60(2):145-157). Annual bluegrass germinates in late summer or fall as soil temperatures fall below 70° F. It continues to germinate throughout winter, allowing several flushes of germination at any one site throughout the season. The life cycles of annual bluegrass and turfgrass are very similar, and annual bluegrass is often more competitive than most turfgrasses. Because annual bluegrass is a grass weed growing with turfgrass, selective control is difficult. Pre-emergent herbicides, such as benefin, bensulide, dithiopyr, oryzalin, oxadiazon, pendimethalin, prodiamine, and benefin/oryzalin, are successful in limiting germination of annual bluegrass. A few post-emergent herbicides reduce Poa annua L. growth, but they could also kill desirable turfgrasses. As such, usage of these post-emergent herbicides are limited. For example, foramsulfuron, sulfosulfuron, and trifloxysulfuron can be used only on warm-season turfgrass. Ethofumesate can be used in dormant bermudagrass, creeping bentgrass, Kentucky bluegrass, tall fescue, perennial ryegrass, and St. Augustine to reduce annual bluegrass infestations. Pronamide can be used in warm-season turfgrass for established annual bluegrass, but it is slow acting. Golf-course managers have few tools to combat Poa annua L. and the invasion of this weed often means that greens must be ripped out and replaced every ten years.
Rough bluegrass (Poa trivialis) is also a cool-season annual grass that is a major weed species. Similar to annual bluegrass, rough bluegrass can outcompete turfgrasses and native plants.
Use of antagonistic microorganisms as bioherbicides against some weeds has been previously reported (Kennedy, et al., 1991, Soil Sci. Soc. Amer. J. 55:722-727; Kennedy, et al., 2001, Weed Sci. 49:792-797; Makowski and Mortensen, 1998, Mycol. Res. 102(12):1545-1552). Xanthomonas campestris pv. poannua is sprayed on plant leaves during mowing and reduces annual bluegrass in bermudagrass. The bacterium enters the plant through the cut leaf and causes systemic wilt, which kills the plant (Johnson, et al., 1996, Weed Technology, 10(3):621-624). A germination arrest factor (GAF) produced by Pseudomonas fluorescens strain WH6 and other related species produce a compound that in-vitro reduced germination of grassy weed species including annual bluegrass (Banowetz, et al., 2008, Biological Control 46:380-390; Banowetz, et al., 2009, Biological Control 50:103-110.) However, P. fluorescens strain WH6 and other related species failed to reduce germination of annual bluegrass in the field. GAF failed to inhibit germination of grassy weed species in the field and the selectivity of GAF is not known.
The physiological characteristics required for a bacterial strain to suppress annual weeds are specific as to (1) the weed growth to be controlled; (2) the specificity of the inhibition is limited to that weed or similar weeds and lack activity against crops or economically important plants; (3) the mode of action of weed control; (4) the activity and ecological niche of the microorganism; and (5) cultural practices and soil and climatic conditions must be favorable for suppressive. Thus, information about microbial treatments for control of weeds other than annual bluegrass cannot be used to predict strains of microorganisms that would reduce annual bluegrass under field conditions or predict criteria for selecting such strains.